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Tooth Staining and Discoloration: a review of literature. Part I: Etiology and Classification

By Dr. Sawsan Nasreddine,Dr. Fida Sayah, Dr. Fady Kassir, and Pr. Mounir Doumit, of the Lebanese University, School of Dentistry

Abstract

Discoloration of the tooth can erode the sparkle from a smile. There are many factors that contribute to tooth staining. It is important to understand that in some cases staining can be prevented but in others it cannot.

There are two types of tooth discoloration: extrinsic which affects teeth from the outside and intrinsic which affects the teeth from the inside.

The purpose of this article is to review literature on the etiologies and classification of tooth staining and discoloration.

The appearance of the dentition is of concern to a large number of people seeking dental treatment and the color of the teeth is of particular cosmetic importance. Tooth discoloration is usually esthetically displeasing and psychologically traumatizing. An understanding of the etiology and classification of tooth discoloration is important to dentists in order to make the correct diagnosis. The correct diagnosis for the cause of discoloration is important as, invariably; it has a profound effect on treatment outcomes.1, 2, 3

Color perception

A basic understanding of the elements of tooth color is important for many aspects of restorative dentistry. Teeth are typically composed of a number of colors and a gradation of color occurs in an individual tooth from the gingival margin to the incisal edge of the tooth.1

The gingival margin often has a darker appearance because of the close approximation of the dentine below the enamel. In most people canine teeth are darker than central and lateral incisors and younger people characteristically have lighter teeth, particularly in the primary dentition.1

The normal color of primary teeth is bluish white whereas color of permanent teeth is grayish white or yellowish white. Color of teeth is determined by translucency and thickness of enamel, color of dentin and pulp. Changes in color of teeth may be physiological/pathological or exogenous/endogenous in nature. With increasing age, enamel becomes thinner because of erosion, and dentin becomes thicker because of deposition of the secondary dentin. Therefore, teeth of elderly persons are usually more yellow or grayish yellow than those of younger persons.4

The viewing conditions are extremely important and variables such as the light source, time of day, surrounding conditions and the angle the tooth is viewed from affect the apparent tooth color.1

Classification

The coronal portion of the tooth consists of enamel, dentine and pulp. Any change to these structures is likely to cause an alteration in the outward appearance of the tooth caused by its light transmitting and reflecting properties. The appearance of tooth color is dependent on the quality of the reflected light and is also, as a consequence, dependent on the incident light.1

Intrinsic discoloration occurs following a change to the structural composition or thickness of the dental hard tissues. The normal color of teeth is determined by the blue, green and pink tints of the enamel and is reinforced by the yellow through the brown shades of dentine beneath. A number of metabolic diseases and systemic factors are known to affect the developing dentition and cause discoloration as a consequence. Local factors such as injury are also recognized: 1, 5

1. Alkaptonuria.

2. Congenital erythropoietic porphyria.

3. Congenital hyperbilirubinaemia.

4. Amelogenesis imperfect.

5. Dentinogenesis imperfect.

6. Tetracycline staining.

7. Fluorosis.

8. Enamel hypoplasia.

9. Pulpal hemorrhagic products.

10. Root resorption.

11. Ageing.1, 5

Extrinsic color discoloration is outside the tooth substance and lies on the tooth surface or in the acquired pellicle.

The origin of the stain may be metallic or non-metallic.1, 5

Internalized discoloration is the incorporation of extrinsic stain within the tooth substance following dental development. It occurs in enamel defects and in the porous surface of exposed dentine.1, 5

Etiology

The etiology of tooth discoloration can be classified according to the location of the stains, either as extrinsic or intrinsic.2

Extrinsic discoloration (table 1)

Etiology of extrinsic staining can be divided into two categories:

a)Direct extrinsic tooth staining: Those compounds which are incorporated into the pellicle and produce a stain as a result of their basic color.

b)Indirect extrinsic tooth staining: Those which lead to staining caused by chemical interaction at the tooth surface.5, 6

Tobacco from cigarettes, cigars, pipes, and chewing tobacco causes tenacious dark brown and black stains that cover the cervical one third to midway on the tooth. Chewing of paan results in the production of blood red saliva that results in a red-black stain on the teeth, gingiva and oral mucosal surfaces.2, 7

Chromogenic bacteria have also been suggested as an etiological factor in the production of stains typically at the gingival margin of the tooth.8 Particular colors of staining are said to be associated with certain mouths, for instance, green and orange (fig.1) in children with poor oral hygiene and black/brown stains (fig.2) in children with good oral hygiene and low caries experience.1, 3, 5 Black stain may be clinically diagnosed as pigmented dark lines parallel to the gingival margin8, 9 or as an incomplete coalescence of dark dots rarely extending beyond the cervical third of the crown.10

Iron supplementation during pregnancy and in childhood may also promote Black stain development.6, 11, 12 The most convincing evidence for the extrinsic method of tooth staining comes from the differing amount of stain found in a comparison of smokers and non-smokers.1, 5, 8

Fig 1: Black stains at the gingival margin of teeth due to chromogenic bacteria

Indirect extrinsic staining of teeth may be associated with occupational exposure to metallic salts and with a number of medicines containing metal salts. The characteristic black staining of teeth in people using iron supplements and iron foundry workers is well documented. Copper causes a green stain in mouth rinses containing copper salts and in workers in contact with the metal in industrial circumstances. A number of other metals have associated colors such as potassium permanganate producing a violet to black color when used in mouth rinses; silver nitrate salt used in dentistry causes a grey color, and stannous fluoride causes a golden brown discoloration.1, 5

The staining effect of prolonged rinsing with chlorhexidine mouth rinses has been documented. A 0.1% chlorhexidine rinse stained slightly more than a 0.2% solution, which produces brown to black discoloration.2, 3, 5

A number of occupation and environmental factors might also be responsible for tooth staining: Industrial exposure to iron, manganese, and silver may stain the teeth black. Mercury and lead dust can cause a blue-green stain; copper and nickel, green to blue-green stain and chromic acid fumes may cause deep orange stain.2, 5

Intrinsic Discoloration (table 2)

These discolorations result from an alteration in the structural composition or thickness of the dental hard tissues. The possible etiology of intrinsic stains includes local and systemic factors.1 Localized injury such as loss of vitality or internal resorption can result in intrinsic staining. Systemic factors can be described as developmental defects such as amelogenesis imperfect and dentinogenesis imperfect, or chronological disturbances including fluorosis, tetracycline and metabolic disorders.7

Besides the pre-eruptive causes for extrinsic discoloration, post-eruption discoloration might occur when the discoloring agent enters the hard tissues either from the pulp or the tooth surface.2

Pre-eruptive causes for intrinsic discoloration

Alkaptonuria: This inborn error of metabolism results in incomplete metabolism of tyrosine and phenylalanine. This affects the permanent dentition by causing a brown discoloration.1, 2, 5

Congenital erythropoietic porphyria: This is a rare, recessive, autosomal, metabolic disorder in which there is an error in porphyrin metabolism leading to the accumulation of porphyrins in bone marrow, red blood cells, urine and teeth. A red-brown discoloration of the teeth is the result and the affected teeth show a red fluorescence under ultra-violet light.1, 2, 5, 13

Congenital hyperbilirubinaemia: The breakdown products of haemolysis will cause a yellow-green discoloration. Mild neonatal jaundice is relatively common, but in rhesus incompatibility massive haemolysis will lead to deposition of bile pigments in the calcifying dental hard tissues, particularly at the neonatal line.1, 2, 5, 14

Amelogenesis imperfect (fig.3): In this hereditary condition, enamel formation is disturbed with regard to mineralization or matrix formation and is classified accordingly. There are 14 different subtypes; the majority is inherited as an autosomal dominant or x-linked trait with varying degrees of expressivity. The appearance varies from the relatively mild hypomature ‘snow-capped’ enamel to the more severe hereditary hypoplasia with thin, hard enamel which has a yellow to yellow-brown appearance.1, 2, 5

Fig 3: Amelogenesis imperfect (Courtesy of Pr. Bacho)

Dentinogenesis imperfect (fig.4): The condition is hereditary and there is no treatment.10

Dentinogenesis imperfect has been classified into three types for diagnostic purposes:

Type I refers to affected teeth in patients who also have osteogenesis imperfect.

Type II refers to affected teeth as an isolated dental trait.

Type III refers exclusively to affected teeth of a racial isolate in southern Maryland, and is known as the “Brandywine Isolate”.15

The main condition related to the dentine alone is Dentinogenesis imperfect II (hereditary opalescent dentine). Both dentitions are affected, the primary dentition usually more severely. The teeth are usually bluish or brown in color, and demonstrate opalescence on transillumination. Once the dentine is exposed, teeth rapidly show brown discoloration, presumably by absorption of chromogens into the porous dentine.1, 2, 5

In this condition, the teeth may be outwardly similar to both types I and II of Dentinogenesis imperfect. Radiographically, the teeth may take on the appearance of ‘shell teeth’ as dentine production ceases after the mantle layer has formed.1, 5

Fig 4: Dentinogenesis imperfect

Post-eruptive causes for intrinsic discoloration

Tetracycline staining: These drugs cross the placenta and can have toxic effects on the developing fetus, and are therefore contraindicated during pregnancy. Toxic effects on the developing fetus include dental discoloration, enamel hypoplasia, and a 40% depression of bone growth. Tetracycline can cause discoloration and enamel hypoplasia of both the primary and permanent dentitions if administered during the period of tooth development. The major factors impacting the amount of tetracycline deposition are dosage, duration of treatment, stage of tooth mineralization, and activity of the mineralization process. The discoloration, which is permanent, varies from yellow or gray to brown depending on the dose or the type of drug received in relation to body weight. After tooth eruption and exposure to light, the fluorescent yellow discoloration gradually changes over a period of months to years to a non fluorescent brown color. The labial surfaces of yellow-stained anterior teeth will darken in time while the palatal surfaces and buccal surfaces of posterior teeth will remain yellow.4, 16, 17

The calcification of deciduous teeth begins at approximately the end of the fourth month of gestation and ends at approximately 11-14 months of age. Permanent teeth begin calcifying after birth and are not affected by exposure to the tetracycline during the prenatal period. The calcification of permanent teeth is completed at 7-8 years of age with the exception of the third molar (“wisdom” teeth). Therefore, the administration of tetracycline to pregnant women must be avoided during the 2nd or 3rd trimester of gestation and to children up to 8 years of age because it may result in discoloration and enamel hypoplasia. The association between staining and enamel hypoplasia as a result of high doses of tetracycline during calcification is possible.4, 16, 17

Minocycline staining is characterized by a blue-gray to gray hue darkening of the crowns and black or green darkening of the roots of erupted teeth. Minocycline differs from other tetracycline in that it is well absorbed from the gastro-intestinal tract and chelates with iron to form insoluble complexes, and this may provoke the tooth staining.4, 16, 17

Miscellaneous: Discoloration is almost impossible to eliminate if caused by silver nitrate or strongly colored iodine solutions in the root canal. Root canal sealers containing iodoform or precipitated silver can also cause discoloration when contracting pulp chamber dentin. Silver points extending into the crown and corroding because of leakage will cause staining. Diamine silver fluoride caused tooth discoloration when used for treatment of dentin hypersensitivity.4

Fluorosis: Dental fluorosis is a condition of enamel hypo mineralization because of the effects of excessive fluoride on ameloblasts during enamel formation. The critical period for clinically significant dental fluorosis in human maxillary central incisors is during the age range of 15 to 30 months. The main consequence of dental fluorosis is compromised esthetics. In its mildest forms, enamel fluorosis appears as loss of translucency at the tip of the summit of the cups of the premolars, molars, or incisal border of the anterior teeth, poorly demarcated opacities, faint white flecks, spots, or striations.18, 19

Fig 5: Discoloration gray-brown after pulp treatment on tooth #11

Enamel hypoplasia: Discoloration (white, yellow, or brown) of enamel and enamel hypoplasia are the most common and milder states of traumatic dental injury. Hypoplasia is characterized by reduced enamel thickness of varying degrees, as well as pits and other irregularities, and although the hardness and transparency of the enamel remain intact, the extent of irregularities varied from tiny spots to large areas, 18 this condition may be localized or generalized. The effect is directly related to the degree of systemic upset. There may be pitting or grooving which predisposes to extrinsic staining of the enamel in the region of tooth disturbed, often then becoming internalized. 5

Pulpal Pathology: Bacterial, mechanical or chemical irritation to the pulp may result in tissue necrosis and the release of disintegration by-products that might penetrate the tubules and discolor the surrounding dentin. Acute trauma to an erupted tooth can cause intrapulpal hemorrhage giving it a reddish tinge. This discoloration can change to gray-brown in a matter of days as the pulp becomes necrotic (fig.5). The translucency of the crown gradually decreases, giving rise to yellowish or yellowish brown discoloration.1, 2, 5

Root resorption: Root resorption is often clinically asymptomatic; however, occasionally the initial presenting feature is a pink appearance at the amelo-cemental junction.1, 2, 5

Dental materials: dental restorations most commonly cause intrinsic discoloration. Amalgam restorations can generate corrosion products, leaving a blue-gray color in the tooth, especially in large cavity preparations with undermined enamel known as amalgam blue. Open margins around composite or glass ionomer restoration may allow chemicals to enter between the restoration and the tooth structure and discolor the underlying dentine.2

Ageing: The natural laying down of secondary dentine affects the light-transmitting properties of teeth resulting in a gradual darkening of teeth with age.1, 5

Conclusion

Tooth discoloration is a frequent dental findings associated with clinical and esthetic problems. It differs in etiology, appearance, composition, location and severity. Knowledge of the etiology of tooth staining is of importance to dentists in order to enable a correct diagnosis to be made when examining a discolored dentition and allows explaining to the patient the exact nature of the condition.5

It is very important for practitioners that the drugs prescribed to pregnant women and to children be free from any adverse effect on teeth. Moreover, there is a significant need for more effective methods to educate health professionals, parents, and children about the harmful/adverse effects of drugs on teeth.5

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Introduction The
problem of inferior alveolar nerve involvement during surgical procedure of the
removal of lower third molars is often a source of litigations1,2,3.
At the same time the impact of this on a person’s quality of life should not be
overlooked. Coronectomy
or partial odontectomy reduces the likelihood of nerve injury by insuring
retention of the vital roots when they are close or associated with the
inferior alveolar nerve as evaluated by plain radiography or CBCT4,5.
The
method aims to remove only the crown part of an impacted mandibular third molar
while leaving the root and pulp undisturbed, thereby avoiding direct or
indirect damage to the inferior alveolar nerve6,7,8. Literature
so far has hailed its merits and many practitioners regularly use the approach
of coronectomy in order to minimise Inferior alveolar nerve injuries. This
technique got in lime light in last decade although r…